Magnesium-nitrogen co-doped carbon dots enhance plant growth through multifunctional regulation in photosynthesis

Herein, we designed and prepared a magnesium and nitrogen co-doped carbon dots (Mg,N-CDs) for plant photosynthesis, in which Mg and N were in carbonate-like and graphite N forms with 5.38% and 3.83% contents, respectively. During a 1-h incubation with chloroplast suspension, Mg,N-CDs entered chloroplasts and transferred energy to them under a xenon lamp, which increased their photosynthetic activity to reduce DCPIP and ferricyanide by up to 52.48% and 41.86%, respectively. After 16 days of foliar spraying, Mg,N-CDs at 300 μg·mL−1 up-regulated the gene expressions of enzymes (15.26–115.02%) related to chlorophyll synthesis and metabolism in rice plants, increasing chlorophyll a and chlorophyll b contents by 14.39% and 26.54%, respectively. The rice seedlings treated with Mg,N-CDs at 300 μg·mL−1 exhibited 109.54%, 104.48%, and 127.16% higher photosynthetic activity, electron transport rate, and photosynthetic efficiency relative to the control, respectively. Moreover, Mg,N-CDs also increased the RuBisCO activity of rice plants by 46.62%. With the energy transformation and physiological regulation, Mg,N-CDs (300 μg·mL−1) increased the height and fresh biomass of rice plants by 22.34% and 70.60%, respectively, through the overall improvement of photosynthesis. This study suggests the great potential of Mg,N-CDs in increasing global agricultural production in the future.